The present invention relates to a control device for volume stream of a hydraulic working medium.
More particularly, it relates to a control device which has for example a working cylinder with a blocking valve having a seat valve body cooperating with a main valve seat in the housing, and a pre-control valve member in operative communication with an actuating element and cooperating with a valve seat provided in the seat valve body under the action of the spring to control the pressure in a pressure chamber formed between the seat valve member and the valve housing.
A control device of the above mentioned general type is disclosed for example in the German document DE-OS 30 42 277. In this control device, by means of a finely controllable locking valve or a so-called lowering valve, the load which for example acts at a consumer during lowering of the associated pressure medium stream does not act ahead. This blocking valve has a seat valve body, in which a pre-control valve member is provided. The pre-control valve member extends with a draw pin into an outflow opening. Such a blocking valve has the disadvantage that the pressure medium can flow out when the control pin of the pre-control valve member extends outwardly of the outflow opening. The actuating path over which an actuating device of the pre-control valve member must move before the pressure medium can flow out is therefore very long.
U.S. Pat. No. 4,741,364 discloses how a load can be raised or lowered via a pre-controlled, complicated control valve which has a main control slider and a pre-control slider. The actuating device is formed as a proportional magnet which acts on the pre-control slider. For regulating the output pressure of the control valve, a complicated force comparison between the forces during the action of a pressure spring and during the action of the pressure is performed. A sequence control between the main control slider and the pre-control slider is not provided.